Switch which reduces rebounding of its contacts



H. MEYER July 20, 19 65 SWITCH YIBICH REDUCES REBOUNDING OF ITS CONTACTS Filed Feb. 10, 1961 2 Sheets-Sheet 1 July 20, 1965 H. MEYER 3,196,231

SWITCH WHICH REDUCES REBOUNDING OF ITS CONTACTS Filed Feb. 10. 3.961 2 Sheets-Sheet 2 Fig.3

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flttome ss United States Patent 3,196,231 SWETCH WHiCH REDUCES REBGUNDING OF ITS CONTACTS Herbert Meyer, Neumunster, Germany, assignor to Licentia Patent-Vern?altungs-G.rn.b.H., Frankfurt am Main, Germany Filed Feb. 10, 1951, Ser. No. 88,470

Claims priority, application Germany, Feb. 12, 1960,

8 Claims. ($1. 200-87) The present invention relates to an electric switch.

More particularly, the present invention relates to an electric switch in which the contacts cooperating with the movable contacts are structurally associated with the stationary part of the actuator system for the movable contacts, and in which, upon closing of the contacts, that part of the switch actuator which causes the movement of the movable contacts strikes the stationary part of the actuator system. In the case of a relay type switch, the actuator system generally consists of a stationary switching magnet and an armature. The armature is connected with a holder which carries the movable contacts, while the stationary switching magnet is mounted on a carrier which supports the cooperating stationary contacts.

The useful life of relays of the above type has to be very high, i.e., the relay Will be called upon to carry out a large number of mechanical and electrical switchings. The electrical life of the switch, i.e., the useful life of the contacts, is to a large extent dependent on the impact of the contacts when the switch is closed.

It is known to dampen contact impact in various Ways, as, for example, by relying on frictional resistances to eliminate or reduce the forces due to the impact of the contacts. It has been found, however, that this will not avoid all the causes of the impact.

One of the causes of the impact occurring upon closing of the switch is the striking of the movable armature against the stationary magnet which is part of the ma netic actuator system of the switch. The impact which this produces is particularly detrimental because it does not occur until some time after the current-carrying contacts have engaged each other, i.e., not until about to 20 milliseconds later, or at a time when the current has already reached a high value, so that the arc-overs which are caused by the rebounding and consequent re-opening of the contacts may produce increased contact scorching or welding (so-called freezing).

The present invention is based on the consideration that it is the higher frequency components of the oscillations produced by the striking of the armature against the magnet which are mainly responsible for the rebounding. The kinetic energy of the movable armature, when it strikes the stationary magnet, is preserved mainly as kinetic energy of the entire magnet, or of the relay as a whole, including the surface or other support upon which it is mounted. A smaller part is converted into oscillatory energy, the oscillations occurring as a mixture of low-frequency components (about 100 cycles per second) and higher-frequency components (about 1000 to 2000 cycles per second).

The higher-frequency components will propagate without appreciable attentuation through all of the stationary structural elements. Thus, oscillatory energy will also be propagated from the point of contact between the movable armature and stationary magnet to the stationary contacts via the stationary magnet, the support for the magnet, and the support carrying the stationary contacts. The stationary contacts will, therefore, undergo a movement which corresponds to this oscillation. The relative low-frequency system, comprising the movable contact and the contact spring, cannot follow the thus-produced high-frequency movements of the stationary contacts, and this results in rebounding which, in turn, produces the above-mentioned undesired opening of the contacts, the latter, of course, causing the above-mentioned arc-overs and freezing.

It is, therefore, a primary object of the present invention to provide a switch which overcomes the above disadvantages. According to the present invention, this is accomplished by keeping away from the stationary contacts the higher-frequency oscillatory energy which is produced when the movable parts of the switch strike against the stationary parts. This can be done, for example, by providing means such as a mechanical low-pass filter in the path of propagation of the oscillatory energy, which filter is arranged between the surface at which these oscillations are produced, namely, the contact surface at which the armature and the stationary magnet engage each other, and the stationary contacts.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic elevational view of a switch according to the present invention.

FIGURE 2 is a sectional view taken substantially along line 22 of FIGURE 1.

FIGURE 3 is a diagrammatic elevational view, partly in section, of another form of the present invention and wherein only a portion of the stationary assembly is shown.

FIGURE 4 is an elevational view similar to FIGURE 3 but showing still another form of the invention.

Referring now to the drawing, the same shows a rela type switch comprising a stationary magnet 1 which is mounted on a support 2. The magnet 1, including its coil 1, is pressed down against the support 2 as, for example, by abutments 3a, 4a, on the supports 3, 4, which carry the stationary contacts 5, 6, these abutments cooperating with movable abut-ments 1a, 1b, carried by the magnet 1, as shown in FIGURE 2. Alternatively, the magnet 1 can be pressed down by an upper dome (not shown) which serves as an arc-extinguishing chamber.

The movable contact assembly 7 comprises an armature 7a and a movable contact carrier 71), the latter supporting contact bridges 9 whose free ends carry the movable contact elements 9a, 9b which engage the stationary contact elements 5a, 6a. Contact springs 8 are provided for pressing the contact bridges 9 downwardly. Compression springs 10 urge the movable contact assembly away from the stationary magnet 1, stationary abutments 10a, 10b being provided for limiting the movement of the movable contact assembly 7.

The switch structure as hereinabove described is known; see, for example, German Patent No. 945,709.

According to the present invention, a mechanical lowpass filter is interposed between the magnet 1 and the support 2 therefor. The low-pass filter comprises a buffer device in the form of one or more heavily prestressed coil springs 12 arranged within a spring casing 11 which is mounted on the support 2, the lower end of the spring abutting against the support 2 and the upper end against the magnet 1. FIGURE 1 shows a one-spring arrangement and FIGURE 3 shows a multiple spring arrangement. In lieu of the compression spring, a prestressed leaf spring 12' may be provided as shown in FIGURE 4.

The magnetic actuator for the relay, namely, the magnet and the armature, form together with the damping spring 12 an oscillatory system. If the natural frequency of this system is made suiiiciently low, it is possible to prevent substantially completely the transmission of highfrequency components, of the mixed frequency oscillations produced by the impact, to the supports 3, 4 and,

"consequently, to the stationary contacts 5, 6 and their the magnet and the spring 12 such that it isapproximately as great as the natural frequency-of the oscillatory systems composedof 'the contactbridges9 and their contact elements9a, and the contact springs 8. Expressed mathematically, the relationship between the mass M of the magnet, the constant C of the damping spring,

the mass M of the movable contact bridge, and the constant C -of the spring which biasses' the contact bridge,

is as follows:

ma 0.; N C If the damping spring 12 is so designed as to meet the above conditions, it is possible that the spring will, due 'to the fact that itstores the kinetic energy of the arma- "ture in the form of potential energy, deflect so much that it will be diflicult to build the switch so as to accommodatethe movement of the magnet. On the other hand, the amplitudes of the oscillations which are to be kept 'away tr'om'the'stationary contacts are relatively small "so that it will be suflicient for the spring to deflect rela- 'tively little.

"Both conditions are met if the spring 12 is given a high initial tension, i.e., if thespring'lZ is prestressed. Thus, the deflections of the spring will remain in spite of low natural frequency of the system.

It has been found that the most advantageous bias of the spring is one which, When the spring 12'converts the kinetic energy of-thearmature intopotential energy, -results in a deflection ofbetween about 0.5 to 1 millimeter.

The above-described mechanical low-pass filter will not ='only keep tliehigher-frequency energycomp'onents away from the stationary contacts, but also the impact of the armaturewill be damped.

It should be noted that it is, known, in general,

to use rubber butters or the'lilrefor damping the impact -on the stationary magnet; existing arrangements, however, do'not have the desired "low-pass filtering effect producedby the present invention.

It will be understood that the above description of the .ipresent-inve'ntion is susceptible to various modifications,

changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I'claim:

'1. In an-electricswi'tch, the combination which commovable contact assembly; a support supporting said mag- "net a'ndsaid stationary contact means; and'means for keeping away from said stationary contact means oscillatory energywhich is higherin frequency than the -natural frequency of the movable contact assembly and whichis p'roduced'upon the impact of said movable contact'assembly against said magnet, saidmeans including a butter device interposed between said support and said magnet, and said bufler device being a low-pass filter,

said movable contact means including a contact spring,

i and the relationship between the mass M of said magnet, the constant C of said buffer device, the mass M of said movable contact means, and constant C of said contact spring being substantially as follows:

2. The combination defined in claim 1 wherein said buii'er device comprises spring means.

3. The combination defined in, claim 2 wherein said buffer device comprises a plurality of spring means.

'4. The combination defined in claim 2 wherein said butler device comprises leaf spring means.

5. The combination defined in claim 2 wherein said buffer device comprises a spring housing for said spring means, said spring housing being mounted on said support and said magnet abutting against saidspring means.

6. The combination defined in claim 1 wherein said bufler device comprises prestressed coil spring means.

'7. The combination defined in-claim 6 wherein said coil spring means are prestressed such an amount that the deflection of said spring means, upon impact of said movable contactassembly against said magnet, will be between about 0.5 and l millimeter.

8. In an electric switch, the combination which comprises: stationary and movable contact means; actuator means for moving said movable contact means relative to said-stationary means, said actuator means including a stationary magnet and a movable armature cooperating with said magnet, said armature being connected to said movable contactmeans and forming therewith a movable contact assembly; a support supporting said magnet and said stationary contact means; and means for keeping away from said stationary contact means oscillatory energy which is higher in frequency than the natural frequency of the movable contact assembly and which is producedupon the impact of said movable contact as sembly against said magnet, said means including a buffer'device interposed between said support and said magnet, and said buffer device being a low-pass filter.

References Cited bythe Examiner UNITED STATES PATENTS 2,544,491 3/51 Davis 20087 2,671,836 3/54 Anger et al 20087 2;688,059 8/54 Holzinger et al. ZOO-91 2,714,141 7 7/55 'Urey et'al 200111 2,727,114 12/55 Kesselring 200l66 2,727,191 1'2/55 Kinsley 317- 2,762,678 9/56 'Moore 248-358 X 2,782,282 2/ 5 7 Schrack '200-91 2,938,094 5/60 Nass 200l66 2,977,438 3/61 'Morschel 200--166 FOREIGN PATENTS 584,050 l/47 Great Britain.

731,713 6/55 Great Britain.

OTHER REFERENCES Switching-Relay Design (Peck and Wagar), published by D. -V an Nostrand Company Inc. (pages 277 and'278 relied on).

BERNARD A. G'ILHEANY, Primary Examiner.

. Y, xam ne 

1. IN AN ELECTRIC SWITCH, THE COMBINATION WHICH COMPRISES: STATIONARY AND MOVABLE CONTACT MEANS; ACTUATOR MEANS FOR MOVING SAID MOVABLE CONTACT MEANS RELATIVE TO SAID STATIONARY MEANS, SAID ACTUATOR MEANS INCLUDING A STATIONARY MAGNET AND A MOVEABLE ARMATURE COOPERATING WITH SAID MAGNET, SAID ARMATURE BEING CONNECTED TO SAID MOVABLE CONTACT MEANS AND FORMING THEREWITH A MOVABLE CONTACT ASSEMBLY; A SUPPORT SUPPORTING SAID MAGNET AND SAID STATIONARY CONTACT MEANS; AND MEANS FOR KEEPING AWAY FROM SAID STATIONARY CONTACT MEANS OSCILLATORY ENERGY WHICH IS HIGHER IN FREQUENCY THAN THE NATURAL FREQUENCY OF THE MOVABLE CONTACT ASSEMBLY AND WHICH IS PRODUCED UPON THE INPACT OF SAID MOVABLE CONTACT ASSEMBLY AGAINST SAID MAGNET, SAID MEANS INCLUDING A BUFFER DEVICE INTERPOSED BETWEEN SAID SUPPORT AND SAID MAGNET, AND SAID BUFER DEVICE BEING A LOW-PASS FILTER, SAID MOVABLE CONTACT MEANS INCLUDING A CONTACT SPRING, AND THE RELATIONSHIP BETWEEN THE MASS MM OF SAID MAGNET, THE CONSTANT CD OF SAID BUFFER DEVICE, THE MASS MC OF SAID MOVABLE CONTACT MEANS, AND CONSTANT CC OF SAID CONTACT SPRING BEING SUBSTANTIALLY AS FOLLOW: 